Do you object to lowering the rails a couple volts, due to the fact that I have lower voltage trafos up the -ss? What would you consider the minimum before we have to start to make changes? I'd ask about the irfp140 but I already know the answer.

Recent discussions on the Aleph-X builders thread involving Nelson Pass and others indicate that 1) a small amount of single ended bias can produce an audible improvement in a complementary follower output stage and 2) that this SE bias can be added passively.

In the F4, connecting a 100 ohm 20W-25W power resistor from the output node to V- would add approximately 5W of SE bias and would be cheap and easy to try.

Perhaps someone who has built an F4 could be talked into trying this and reporting back (Steen?)